/* -------------------------------------------------------------------------
 *
 * off.h
 *	  openGauss disk "offset" definitions.
 *
 *
 * Portions Copyright (c) 1996-2012, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/include/storage/off.h
 *
 * -------------------------------------------------------------------------
 */
#ifndef OFF_H
#define OFF_H

#include "storage/item/itemid.h"
/*
 * OffsetNumber:
 *
 * this is a 1-based index into the linp (ItemIdData) array in the
 * header of each disk page.
 */
typedef uint16 OffsetNumber;

#define InvalidOffsetNumber ((OffsetNumber)0)
#define FirstOffsetNumber ((OffsetNumber)1)
#define MaxOffsetNumber ((OffsetNumber)(BLCKSZ / sizeof(ItemIdData)))
#define OffsetNumberMask (0xffff) /* valid uint16 bits */

/* ----------------
 *		support macros
 * ----------------
 */

/*
 * OffsetNumberIsValid
 *		True iff the offset number is valid.
 */
#define OffsetNumberIsValid(offsetNumber) \
    ((bool)((offsetNumber != InvalidOffsetNumber) && (offsetNumber <= MaxOffsetNumber)))

/*
 * OffsetNumberNext
 * OffsetNumberPrev
 *		Increments/decrements the argument.  These macros look pointless
 *		but they help us disambiguate the different manipulations on
 *		OffsetNumbers (e.g., sometimes we subtract one from an
 *		OffsetNumber to move back, and sometimes we do so to form a
 *		real C array index).
 */
#define OffsetNumberNext(offsetNumber) ((OffsetNumber)(1 + (offsetNumber)))
#define OffsetNumberPrev(offsetNumber) ((OffsetNumber)(-1 + (offsetNumber)))

#endif /* OFF_H */
